The present invention generally relates to a transmission, and more specifically to a method and apparatus for operating a transmission coupled to an engine for enhanced fuel efficiency characteristics.
Most engines are configured to operate along a torque curve which optimizes the power output of the engine. Under heavy load conditions, it generally is desirable to operate along this optimized power torque curve. However, under some operating conditions, it is not desirable to operate along the optimized power torque curve. In particular, under low load conditions, the engine may not need the maximum power capabilities of the engine and it may be desirable to operate along torque curve which optimizes fuel efficiency as opposed to power.
It is possible to collect fuel efficiency data for a specific engine and to map out the fuel consumption for a given engine speed and torque. Using this fuel efficiency data, a torque curve can be determined which follows a path of greatest fuel efficiency as the engine accelerates from low speed to high speed. The engine can operate along this maximum efficiency torque curve by limiting the flow of fuel supplied to the engine. This maximum efficiency torque curve can vary considerable from the maximum power torque curve generally used. A drawback of altering the shape of the torque curve is that transmission shift points used while operating along the torque curve optimized for maximum power may not be suitable when operating along the torque curve optimized for maximum efficiency.
What is needed therefore is a method for determining the maximum efficiency torque curve and an apparatus for controlling a transmission coupled to an engine having enhanced the fuel efficiency characteristics which overcomes the above-mentioned drawbacks.
In accordance with a first embodiment of the present invention, there is provided a drive line assembly for a work machine. The drive line assembly includes an engine driving an engine output shaft and an engine speed sensor which generates engine speed signals indicative of a speed of the engine output shaft. The drive line assembly further includes a fuel injector operable to regulate fuel flow to the engine and a transmission driven by the engine output shaft and having a number of gear ratios. The drive line assembly yet further includes a controller operable to store a predetermined maximum efficiency curve of engine speed versus torque output and determine the engine speed from the engine speed signals. The controller is further operable to limit the fuel flow the fuel injector supplies to the engine to cause the engine to operate along the predetermined maximum efficiency curve for the engine speed. The controller is yet further operable to control shift points between the number of gear ratios based on the predetermined maximum efficiency curve.
In accordance with a second embodiment of the present invention, there is provided a method for controlling a drive line assembly. The drive line assembly includes an engine driving an engine output shaft and an engine speed sensor which generates engine speed signals indicative of a speed of the engine output shaft. The drive line assembly further includes a fuel injector operable to regulate fuel flow to the engine, a transmission driven by the engine output shaft and having a number of gear ratios, and a controller. The method includes the steps of storing a predetermined maximum efficiency curve of engine speed versus torque output and determining the engine speed from the engine speed signals. The method further includes the steps of limiting fuel flow the fuel injector supplies to the engine to cause the engine to operate along the predetermined maximum efficiency curve for the engine speed and controlling shift points between the number of gear ratios based on the predetermined maximum efficiency curve.